Temporal evolution of under ice reflectivity

Multiyear Arctic Sea ice is a heterogeneous material whose acoustic properties are functions of time and space. Over the past few years a number of investigators have studied the reflectivity of sound at the ice-water interface for sound incident from the water. The studies have considered reflections of low- and high-frequency sound for fixed times of the year. From data collected in a recent year-long field experiment conducted in the Arctic, the reflection coefficient at the ice-water interface for sound incident from the water column has been determined as a function of time. The purpose of this paper is to study the temporal evolution of the reflection coefficient with a view to explain the observed fluctuations in the magnitude of the reflection coefficient. A thermodynamic model of ice growth was used to obtain the temperature and salinity structure of the ice for each month of the year and an elastic model was used to calculate the corresponding compressional and shear wave speeds. The reflection coefficient was calculated and the results were compared for various changes in the input parameters to the models. Correlation exists between the model and field measurements of reflection coefficient during the months of September-April. The model does not predict the behavior observed during June-August. It is believed that the reason for the discrepancy is associated with a change in water column properties during this time. (C) 1996 Acoustical Society of America.